JP4172585B2 - A method for obtaining a thermal barrier with bending flexibility. - Google Patents

Description

  The present invention provides a thermal barrier with flexo-adaptives, ie, substrate deformation under the influence of a thermal gradient, whether due to mechanical or dilatometrics. Relates to a thermal barrier having sufficient flexibility to accommodate In particular, the present invention relates to an economical method for obtaining such a thermal barrier by means of a thermal injection.

Today, turbine engine components that are exposed to hot combustion gas streams are made of superalloys that withstand high temperatures and are protected from heat and corrosion by a coating called a thermal barrier. at present,
The thermal barrier is generally an alumina underlayer of NiPtAl or MCrAlY (M = Fe, Ni, Co and NiCo) that forms a chemical barrier to oxidation and corrosion;
・ Heat-insulating ceramic layer ZrO ₂ -YO
It consists of.

  Hereinafter, for convenience, a direction substantially perpendicular to the component surface on which the thermal barrier is applied is referred to as “vertical”.

  Similarly, the direction almost in contact with the part surface on which the thermal barrier is applied is called “horizontal”.

The ceramic layer is generally deposited in multiple passes or paths or processes by thermal injection, for example using a plasma arc torch. In each pass, a ceramic base layer with a thickness of 5 μm to 40 μm is typically deposited, and the number of base layers applied in this way determines the thickness of the entire coating. This way
・ It is easier to control the coating thickness,
Relieve the heating of the thermal barrier, thereby avoiding refection cracking and peeling during cooling.

However, this method has the following two drawbacks.
-The ceramic layer has little flexibility along the tangential direction of the surface of the part. As a result, the thermal barrier thus obtained cannot sufficiently withstand a large thermal shock at, for example, the blade position of the turbine, and these thermal barriers will be peeled off soon.
・ A micro weld is formed when molten ceramic droplets reach the previously deposited and partially cooled ceramic, and bonding is performed by this micro weld, so the vertical connection between the basic layers is incomplete. is there. For this reason, the ceramic basic layer constituting such a thermal barrier tends to be separated by the action of thermal shock, and similarly the thermal barrier is peeled off.

  Therefore, the thermal barrier obtained by plasma injection in this way is dedicated to fixed parts that do not suffer from thermal shock as in the combustion chamber. In this case, the ceramic layer is about 0.3 mm, and its service life is completely suppressed.

  In order to better protect the combustion chamber of the turbojet engine from heat, a thick thermal barrier by plasma injection, ie a thermal barrier with a thickness of 1 mm or more has been developed. In this application, it is necessary to make a vertical crack in the thickness of the ceramic deposit so that the deposit is flexible in the horizontal direction, ie tangential to the part surface. Without such a unidirectional crack network, the thermal stress at the edge of the deposit becomes too high, resulting in the thermal barrier peeling during use.

  In this regard, U.S. Pat. No. 5,073,433 deposits a ceramic layer by thermal injection in multiple successive passes, deposits a material layer of approximately 5 μm in each pass, and cools after each pass to form a vertical crack. The specification is known.

However, this method has the following two drawbacks.
• Coating with multiple passes separated by a cooling step has additional costs.
This method has the disadvantages often seen with multilayer coatings as described above. That is, since the connection by the micro welds between the base layers is incomplete, separation of these base layers and peeling of the thermal barrier are promoted. This disadvantage is exacerbated by the cooling of the deposits that takes place between each base layer.

  Also, from US Pat. No. 6,306,517, a method for adding a thermal barrier to a thin layer by plasma injection is known, and the bonding between layers is improved by columnar nucleation of crystal grains. Thus, the crystal grains can be shared by a plurality of layers. Unfortunately, such a method reduces the flexibility of the thermal barrier because nucleation also occurs laterally.

  Today, a deposition method called “vapor deposition”, in particular, EBPVD (Electron Beam Physical Vapor Deposition) is known. The ceramic layer obtained here takes the form of an adjacent thin vertical column joined to the lower layer by its bottom. For reference, these columns are about 5 μm in diameter. By such a method, it is possible to obtain a thermal barrier of excellent quality which is excellent in flexibility in the horizontal direction and firmly bonded in the vertical direction and as a result is strong against thermal shock.

However, this method has the following two drawbacks.
-Vapor deposition is time consuming and expensive.
・ Corrosive hot combustion gas reaches a very large number of lower layers between pillars, but the lower layers gradually corrode to break and peel off the thermal barrier. The number of years is limited.

  It should be noted that in general, the tendency of the thermal barrier to flake increases with the protrusions of parts having a small radius of curvature, and thus with small parts such as turbine blades.

  Furthermore, in order to obtain a thermal barrier with the smallest possible tendency to delaminate, it is necessary to obtain a thermal barrier with high adhesion of materials and the strongest connectivity.

US Pat. No. 5,073,433 US Pat. No. 6,306,517

  The first problem to be solved is to increase the peel strength of the thermal barrier.

  The second problem to be solved is to reduce the cost of generating the thermal barrier.

  In order to withstand the high thermal effects of the substrate surface and the strong mechanical action of the substrate, and precisely by doing so, the thermal barrier is tangential to the surface covered by this thermal barrier. Must be flexible. This requires the formation of vertical cracks extending from the surface of the thermal barrier to the substrate or underlayer, ie cracks that penetrate the entire ceramic layer.

  The present invention proposes a method of obtaining a bendable thermal barrier, which includes at least an 80 μm ceramic layer (44) deposited on a substrate (40) covered by an underlayer (42). The ceramic layer (44) is deposited by thermal injection using a so-called “plasma arc” torch (30), the action of which is torch power, material flow rate, torch and coated part (10) It is determined by the distance and the moving speed of the torch with respect to the part.

  Such a method consists of directly depositing the ceramic layer on the lower layer in one single pass while keeping the spray distance from 20 mm to 90 mm, and the moving speed of the torch is 2 mm / sec to 10 mm / sec, The flow rate was 40 g / min to 100 g / min, and the arc strength of the torch was 500 A to 800 A, and after cooling, at least two nearly vertical cracks per millimeter penetrating the entire ceramic layer were obtained. It is characterized by.

  The power of the torch is adjusted to the high value at which the ceramic layer is formed in a single pass, and the ceramic particles are welded vertically, as new drops of molten material still reach the very hot material. Has been well bonded. This is facilitated by selecting the torch moving speed as slow as possible, preferably 2 mm / sec to 10 mm / sec. Thus, the temperature at the location of the deposit increases, thereby resulting in a horizontal microcrack, exfoliation, and a dense microstructure with a small number of fines, increasing the cohesion or cohesion of the material. It is done. Single pass injection is an important parameter directly intervening in the thermal barrier peel strength. In fact, when the material is sprayed in multiple passes, the adhesion between the multiple material layers deposited in each pass is lower than the adhesion within the same layer. In that case, a horizontal crack may start between the two layers, which impairs the resistance of the thermal barrier.

  Moreover, since the ceramic layer formed by the jet is very hot, when the jet moves, the thermal barrier comes into contact with the surrounding air and the thermal gradient in the vertical direction increases. This thermal gradient promotes the formation of cracks on the surface of the ceramic layer, which then spread vertically to the lower layer and penetrate the entire ceramic layer.

  The inventor has confirmed that these two phenomena appear simultaneously. If the power is too low, the crack spacing will be very irregular and the vertical coupling between the particles of the material will be moderate. Increasing the power of the torch will increase the crack density and homogeneity, while improving the vertical coupling between the particles. The inventor has obtained a thermal barrier with a satisfactory peel resistance up to a 250 μm thick ceramic layer with sufficient power, i.e. sufficiently strong to obtain a crack density at least equal to the required value. The optimum quality is located between 100 μm and 150 μm. It should be noted that the proper torch parameters to achieve this result depend on a number of parameters such as the ceramic used, component heat dissipation, powder flow rate, jet width, torch loss factor, and the like.

  It should also be noted that, on the one hand, those skilled in the art will limit the power of the torch so as not to generate excessive heating that can lead to melting of the substrate or unacceptable degradation of the particle structure of the substrate.

  The size of the cracks as well as the number of cracks per mm depends on the thickness of the deposit. The thicker the deposit, the wider the crack and the fewer per mm.

  The thickness of the ceramic layer obtained in a single pass will, of course, depend on the material flow rate, the distance between the torch and the part, and the moving speed of the torch or jet relative to the part, and the loss factor of the torch. Thus, the thickness of the ceramic layer increases with the flow rate of the material, but as the distance or speed increases, this thickness decreases. Those skilled in the art will experiment to define these parameters on a case-by-case basis, depending on the material being deposited.

  The present invention also proposes applying the above method to the blades of a turbojet engine including a wing and a base and applying a ceramic layer to the wing.

Such a method is
a. Holding the base (14) of the blade (10) by means of a tool (20) rotating at a rotational speed V about the geometric axis (16);
b. Subjecting the wing (12) to the jet (32) of the torch (30) in which a relative movement D1 parallel to the geometric axis (16) and a relative movement D2 perpendicular to the geometric axis (16) takes place;
c. The blade (10) is centered about the geometric axis (16), consisting of jetting ceramics by moving the jet (32) only once from one end (18a, 18b) to the other end (18b, 18a) of the wing. So that the torch (30) moves according to D2 and stays at a certain distance from the surface of the blade (12), and the torch (30) moves according to D1 to the width of the jet (32). A spiral ceramic layer (44) having an equal pitch is formed on the surface of the blade (12).

  The present invention will be further understood from detailed embodiments of the method and the accompanying drawings, and the advantages obtained by the present invention will become more apparent.

  Reference is first made to FIG.

The component covering the thermal barrier is a turbine blade 10 made of a superalloy mainly composed of nickel that influences solidification. The thermal barrier comprises a MCrAlY underlayer coated with a 125 μm ceramic layer of zircon ZrO ₂ containing 8% yttrium Y ₂ O ₃ .

  The blade 12 of the blade 10 is covered with a lower layer of MCrAlY deposited according to the usual method.

  The blade 10 is then held on the mount 20 by the base 14. The mount can rotate the vanes about the axis 16, i.e., the vanes can themselves rotate with respect to the longitudinal direction, and the vanes 12 are provided in front of the plasma torch 30. The plasma torch jet is indicated by reference numeral 32. The plasma torch 32 is here a model F4 commercialized by Sultzer Meto.

  The torch is placed 50 mm from the blade 10 and the blade 10 is then rotated about the shaft 16. The torch 30 is activated and the jet 32 first strikes the top 18 a of the blade 10 and gradually moves toward the base 14 to reach the other end 18 b of the blade 12, thus winding around the surface of the blade 10. Are formed to form a spiral ceramic layer 44. The jet 32 moves at the resulting speed of 6 mm / sec on the surface of the blade 12. The flow rate of the powder is 70 g / min, and the power of the torch is obtained at an arc intensity of 700A. The adjustment of the torch is a so-called “high temperature”, and the deposition temperature is 550 ° C. This temperature is measured immediately after passage of the jet 32 at the deposition surface 10 mm behind the jet.

  Reference is now made to FIG.

  The substrate, the lower layer, and the ceramic layer thus obtained are indicated by reference numerals 40, 42 and 44, respectively. The crack is indicated by reference numeral 50. In this microstructure, 4.8 cracks are counted per mm, and the average distance is 200 μm. As this micrograph shows, the crack 50 is substantially vertical, ie, substantially perpendicular to the substrate 40. The two edges of the crack 50 may be parallel or open towards the surface or lower layer 42. The most important feature of the crack 50 is that the crack progresses from the surface to the lower layer 42 by penetrating the entire thickness of the ceramic layer 44, as can be seen from the microstructural chart.

  Reference is now made to FIG.

  In this microstructural chart, it can be seen that the cracks 50 are locally irregular but statistically form a homogeneous anisotropic lattice. These cracks 50 provide the thermal barrier with the required flexibility along the tangential surface of the substrate 40. Crack density is defined as the average number of cracks per mm across any geometric line.

It is a figure which shows the deposition of the ceramic layer by a plasma torch. It is sectional drawing of the microstructure of the thermal barrier obtained in this way. It is a figure which shows the microstructure of the surface of a thermal barrier.

Explanation of symbols

10 Parts or blades 12 Wings 14 Base 16 Geometric axes 18a, 18b Wing tips 30 Torch 32 Jet 40 Substrate 42 Lower layer 44 Ceramic layer 50 Crack

Claims (2)

A method for obtaining a thermal barrier with bending flexibility, said thermal barrier comprising a ceramic layer (44) of at least 80 μm deposited on a substrate (40) covered by an underlayer (42), said ceramic The layer (44) is deposited by thermal injection using a so-called “plasma arc” torch (30), the action of the torch being the power of this torch, the flow rate of the material, the distance between the torch and the coated part (10), Determined by the moving speed of the torch relative to the part,
It consists of depositing the ceramic layer directly on the lower layer in one single pass while keeping the spray distance from 20 mm to 90 mm, the torch moving speed from 2 mm / sec to 10 mm / sec, and the material flow rate from 40 g / min A method characterized in that at least two substantially vertical cracks per millimeter penetrating through the entire ceramic layer are obtained after cooling by setting the arc intensity of the torch from 500 A to 800 A at 100 g / min. The component (10) is a vane having a geometric axis (16) comprising a wing (12) and a base (14), and the ceramic layer (44) is applied to the wing (12);
a. Holding the base (14) of the blade (10) by means of a tool (20) rotating at a rotational speed V about the geometric axis (16);
b. Subjecting the wing (12) to the jet (32) of the torch (30) in which a relative movement D1 parallel to the geometric axis (16) and a relative movement D2 perpendicular to the geometric axis (16) is performed;
c. The jet (32) is moved only once from one end (18a, 18b) of the wing to the other end (18b, 18a) to inject ceramic, and the blade (10) is connected to the geometric axis (16 ), The torch (30) moves according to D2 so that it stays at a certain distance from the surface of the blade (12), and the torch (30) moves according to D1 to move the jet ( The method according to claim 1, characterized in that a spiral ceramic layer (44) is formed on the surface of the blade (12) with a pitch equal to the width of 32).

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